Uplink demodulation reference signal design for mimo transmission

ABSTRACT

A base station capable of communicating with a plurality of subscriber stations is provided. The base station transmits control information and data to at least one of the plurality of subscriber stations in a subframe using a subset of antenna ports corresponding to a subset of antenna port numbers. The base station maps reference signals corresponding to the subset of antenna ports according to a transmission rank R. The base station indicates, via a cyclic shift indicator (CSI) field in an uplink grant, an assigned resource index corresponding to the mapped reference signal. The CSI field includes a cyclic shift and an orthogonal cover code (OCC) index. The subscriber station uses a resource mapping table to identify the assigned resource index based on the transmission rank, cyclic shift and OCC index.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

The present application is related to U.S. Provisional PatentApplication No. 61/291,717, filed Dec. 31, 2009, entitled “UPLINKDEMODULATION REFERENCE SIGNAL DESIGN FOR MIMO TRANSMISSION” and U.S.Provisional Patent Application No. 61/360,363, filed Jun. 30, 2010,entitled “UPLINK DEMODULATION REFERENCE SIGNAL DESIGN FOR MIMOTRANSMISSION. Provisional Patent Application Nos. 61/291,717 and61/360,363 are assigned to the assignee of the present application andare hereby incorporated by reference into the present application as iffully set forth herein. The present application hereby claims priorityunder 35 U.S.C. §119(e) to U.S. Provisional Patent Application Nos.61/291,717 and 61/360,363.

TECHNICAL FIELD OF THE INVENTION

The present application relates generally to wireless communicationsand, more specifically, to a system and method for transmitting downlinkreference signals in a multi-user multiple input multiple output system.

BACKGROUND OF THE INVENTION

Modern communications demand higher data rates and performance.Multiple-input multiple-output (MIMO) antenna systems, also known asmultiple-element antenna (MEA) systems, achieve greater spectralefficiency for allocated radio frequency (RF) channel bandwidths byutilizing space or antenna diversity at both the transmitter and thereceiver, or in other cases, the transceiver.

In MIMO systems, each of a plurality of data streams is individuallymapped and modulated before being precoded and transmitted by differentphysical antennas or effective antennas. The combined data streams arethen received at multiple antennas of a receiver. At the receiver, eachdata stream is separated and extracted from the combined signal. Thisprocess is generally performed using a minimum mean squared error (MMSE)or MMSE-successive interference cancellation (SIC) algorithm.

Additionally, a downlink physical signal corresponds to a set ofresource elements used by the physical layer but does not carryinformation originating from higher layers. The following downlinkphysical signals are defined: Synchronization signal and Referencesignal.

The reference signal consists of known symbols transmitted at a welldefined OFDM symbol position in the slot. This assists the receiver atthe user terminal in estimating the channel impulse response tocompensate for channel distortion in the received signal. There is onereference signal transmitted per downlink antenna port and an exclusivesymbol position is assigned for an antenna port (when one antenna porttransmits a reference signal other ports are silent). Reference signals(RS) are used to determine the impulse response of the underlyingphysical channels.

SUMMARY OF THE INVENTION

A base station capable of communicating with a plurality of subscriberstations is provided. The base station includes a transmit path. Thetransmit path includes circuitry configured to: transmit controlinformation and data to at least one of the plurality of subscriberstations in a subframe; transmit a plurality of resource blocks in thesubframe; transmit the data using a subset of antenna portscorresponding to a subset of antenna port numbers; map reference signalscorresponding to the subset of antenna ports according to a transmissionrank R; and indicate, via a cyclic shift indicator (CSI) field in anuplink grant, an assigned resource index corresponding to the mappedreference signal. The CSI field includes a cyclic shift and anorthogonal cover code (OCC) index.

A subscriber station capable of communicating with at least one basestation is provided. The subscriber station includes a receiverconfigured to receive control information and data from at least one ofthe plurality of base stations in a subframe. The receiver is configuredto receive a plurality of resource blocks in the subframe. Thesubscriber station also includes a controller configured to identify, ina cyclic shift indicator (CSI) field in an uplink grant, an assignedresource index corresponding to a reference signal mapped correspondingto a subset of antenna ports according to a transmission rank R. The CSIfield includes a cyclic shift and an orthogonal cover code (OCC) index.The controller is also configured to cause the receiver to receive thedata using a subset of antenna ports corresponding to the subset ofantenna port numbers and identify the mapped reference signals.

A method operating a base station capable of communicating with aplurality of subscriber stations is provided. The method includestransmitting control information and data to at least one of theplurality of subscriber stations in a subframe; transmitting a pluralityof resource blocks in the subframe; and transmitting the data using asubset of antenna ports corresponding to the subset of antenna portnumbers. The method also includes mapping reference signalscorresponding to the subset of antenna ports according to a transmissionrank R; and indicating, via a cyclic shift indicator (CSI) field in anuplink grant, an assigned resource index corresponding to the mappedreference signal. The CS field comprising a cyclic shift and anorthogonal cover code (OCC) index.

Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, itmay be advantageous to set forth definitions of certain words andphrases used throughout this patent document: the terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation; the term “or,” is inclusive, meaning and/or; the phrases“associated with” and “associated therewith,” as well as derivativesthereof, may mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like; and theterm “controller” means any device, system or part thereof that controlsat least one operation, such a device may be implemented in hardware,firmware or software, or some combination of at least two of the same.It should be noted that the functionality associated with any particularcontroller may be centralized or distributed, whether locally orremotely. Definitions for certain words and phrases are providedthroughout this patent document, those of ordinary skill in the artshould understand that in many, if not most instances, such definitionsapply to prior, as well as future uses of such defined words andphrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates an exemplary wireless network, which transmitsACK/NACK messages according to an exemplary embodiment of thedisclosure;

FIG. 2A illustrates a high-level diagram of an orthogonal frequencydivision multiple access transmit path according to an exemplaryembodiment of the disclosure;

FIG. 2B illustrates a high-level diagram of an orthogonal frequencydivision multiple access receive path according to an exemplaryembodiment of the disclosure;

FIG. 3 illustrates an exemplary wireless subscriber station according toembodiments of the present disclosure; and

FIG. 4 illustrates separate downlink reference modulation signal (DMRS)sequences with different lengths according to embodiments of the presentdisclosure.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 4, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged wireless communications system.

FIG. 1 illustrates an exemplary wireless network 100, which transmitsACK/NACK messages according to the principles of the present disclosure.In the illustrated embodiment, wireless network 100 includes basestation (BS) 101, base station (BS) 102, base station (BS) 103, andother similar base stations (not shown). Base station 101 is incommunication with base station 102 and base station 103. Base station101 is also in communication with Internet 130 or a similar IP-basednetwork (not shown).

Base station 102 provides wireless broadband access (via base station101) to Internet 130 to a first plurality of subscriber stations withincoverage area 120 of base station 102. The first plurality of subscriberstations includes subscriber station 111, which may be located in asmall business (SB), subscriber station 112, which may be located in anenterprise (E), subscriber station 113, which may be located in awireless fidelity (WiFi) hotspot (HS), subscriber station 114, which maybe located in a first residence (R), subscriber station 115, which maybe located in a second residence (R), and subscriber station 116, whichmay be a mobile device (M), such as a cell phone, a wireless laptop, awireless PDA, or the like.

Base station 103 provides wireless broadband access (via base station101) to Internet 130 to a second plurality of subscriber stations withincoverage area 125 of base station 103. The second plurality ofsubscriber stations includes subscriber station 115 and subscriberstation 116. In an exemplary embodiment, base stations 101-103 maycommunicate with each other and with subscriber stations 111-116 usingOFDM or OFDMA techniques.

Base station 101 may be in communication with either a greater number ora lesser number of base stations. Furthermore, while only six subscriberstations are depicted in FIG. 1, it is understood that wireless network100 may provide wireless broadband access to additional subscriberstations. It is noted that subscriber station 115 and subscriber station116 are located on the edges of both coverage area 120 and coverage area125. Subscriber station 115 and subscriber station 116 each communicatewith both base station 102 and base station 103 and may be said to beoperating in handoff mode, as known to those of skill in the art.

Subscriber stations 111-116 may access voice, data, video, videoconferencing, and/or other broadband services via Internet 130. In anexemplary embodiment, one or more of subscriber stations 111-116 may beassociated with an access point (AP) of a WiFi WLAN. Subscriber station116 may be any of a number of mobile devices, including awireless-enabled laptop computer, personal data assistant, notebook,handheld device, or other wireless-enabled device. Subscriber stations114 and 115 may be, for example, a wireless-enabled personal computer(PC), a laptop computer, a gateway, or another device.

FIG. 2A is a high-level diagram of an orthogonal frequency divisionmultiple access (OFDMA) transmit path. FIG. 2B is a high-level diagramof an orthogonal frequency division multiple access (OFDMA) receivepath. In FIGS. 2A and 2B, the OFDMA transmit path is implemented in basestation (BS) 102 and the OFDMA receive path is implemented in subscriberstation (SS) 116 for the purposes of illustration and explanation only.However, it will be understood by those skilled in the art that theOFDMA receive path may also be implemented in BS 102 and the OFDMAtransmit path may be implemented in SS 116.

The transmit path in BS 102 comprises channel coding and modulationblock 205, serial-to-parallel (S-to-P) block 210, Size N Inverse FastFourier Transform (IFFT) block 215, parallel-to-serial (P-to-S) block220, add cyclic prefix block 225, up-converter (UC) 230, a referencesignal multiplexer 290, and a reference signal allocator 295. Thereceive path in SS 116 comprises down-converter (DC) 255, remove cyclicprefix block 260, serial-to-parallel (S-to-P) block 265, Size N FastFourier Transform (FFT) block 270, parallel-to-serial (P-to-S) block275, channel decoding and demodulation block 280.

At least some of the components in FIGS. 2A and 2B may be implemented insoftware while other components may be implemented by configurablehardware or a mixture of software and configurable hardware. Inparticular, it is noted that the FFT blocks and the IFFT blocksdescribed in this disclosure document may be implemented as configurablesoftware algorithms, where the value of Size N may be modified accordingto the implementation.

Furthermore, although this disclosure is directed to an embodiment thatimplements the Fast Fourier Transform and the Inverse Fast FourierTransform, this is by way of illustration only and should not beconstrued to limit the scope of the disclosure. It will be appreciatedthat in an alternate embodiment of the disclosure, the Fast FourierTransform functions and the Inverse Fast Fourier Transform functions mayeasily be replaced by Discrete Fourier Transform (DFT) functions andInverse Discrete Fourier Transform (IDFT) functions, respectively. Itwill be appreciated that for DFT and IDFT functions, the value of the Nvariable may be any integer number (i.e., 1, 2, 3, 4, etc.), while forFFT and IFFT functions, the value of the N variable may be any integernumber that is a power of two (i.e., 1, 2, 4, 8, 16, etc.).

In BS 102, channel coding and, modulation block 205 receives a set ofinformation bits, applies coding (e.g., LDPC coding) and modulates(e.g., QPSK, QAM) the input bits to produce a sequence offrequency-domain modulation symbols. Serial-to-parallel block 210converts (i.e., de-multiplexes) the serial modulated symbols to paralleldata to produce N parallel symbol streams where N is the IFFT/FFT sizeused in BS 102 and SS 116. Size N IFFT block 215 then performs an IFFToperation on the N parallel symbol streams to produce time-domain outputsignals. Parallel-to-serial block 220 converts (i.e., multiplexes) theparallel time-domain output symbols from Size N IFFT block 215 toproduce a serial time-domain signal. Add cyclic prefix block 225 theninserts a cyclic prefix to the time-domain signal. Finally, up-converter230 modulates (i.e., up-converts) the output of add cyclic prefix block225 to RF frequency for transmission via a wireless channel. The signalmay also be filtered at baseband before conversion to RF frequency. Insome embodiments, reference signal multiplexer 290 is operable tomultiplex the reference signals using code division multiplexing (CDM)or time/frequency division multiplexing (TFDM). Reference signalallocator 295 is operable to dynamically allocate reference signals inan OFDM signal in accordance with the methods and system disclosed inthe present disclosure.

The base station 102 can enable (e.g., activate) all of its antennaports or a subset of antenna ports. For example, when BS 102 includeseight antenna ports, BS 102 can enable four of the antenna ports for usein transmitting information to the subscriber stations. It will beunderstood that illustration of BS 102 enabling four antenna ports isfor example purposes only and that any number of antenna ports could beactivated.

The transmitted RF signal arrives at SS 116 after passing through thewireless channel and reverse operations to those at BS 102 areperformed. Down-converter 255 down-converts the received signal tobaseband frequency and remove cyclic prefix block 260 removes the cyclicprefix to produce the serial time-domain baseband signal.Serial-to-parallel block 265 converts the time-domain baseband signal toparallel time domain signals. Size N FFT block 270 then performs an FFTalgorithm to produce N parallel frequency-domain signals.Parallel-to-serial block 275 converts the parallel frequency-domainsignals to a sequence of modulated data symbols. Channel decoding anddemodulation block 280 demodulates and then decodes the modulatedsymbols to recover the original input data stream.

Each of base stations 101-103 may implement a transmit path that isanalogous to transmitting in the downlink to subscriber stations 111-116and may implement a receive path that is analogous to receiving in theuplink from subscriber stations 111-116. Similarly, each one ofsubscriber stations 111-116 may implement a transmit path correspondingto the architecture for transmitting in the uplink to base stations101-103 and may implement a receive path corresponding to thearchitecture for receiving in the downlink from base stations 101-103.

FIG. 3 illustrates an exemplary wireless subscriber station according toembodiments of the present disclosure. The embodiment of wirelesssubscriber station 116 illustrated in FIG. 3 is for illustration only.Other embodiments of the wireless subscriber station 116 could be usedwithout departing from the scope of this disclosure.

Wireless subscriber station 116 comprises antenna 305, radio frequency(RF) transceiver 310, transmit (TX) processing circuitry 315, microphone320, and receive (RX) processing circuitry 325. SS 116 also comprisesspeaker 330, main processor 340, input/output (I/O) interface (IF) 345,keypad 350, display 355, and memory 360. Memory 360 further comprisesbasic operating system (OS) program 361 and a plurality of applications362. The plurality of applications can include one or more of resourcemapping tables (Tables 1-10 described in further detail herein below).

Radio frequency (RF) transceiver 310 receives from antenna 305 anincoming RF signal transmitted by a base station of wireless network100. Radio frequency (RF) transceiver 310 down-converts the incoming RFsignal to produce an intermediate frequency (IF) or a baseband signal.The IF or baseband signal is sent to receiver (RX) processing circuitry325 that produces a processed baseband signal by filtering, decoding,and/or digitizing the baseband or IF signal. Receiver (RX) processingcircuitry 325 transmits the processed baseband signal to speaker 330(i.e., voice data) or to main processor 340 for further processing(e.g., web browsing).

Transmitter (TX) processing circuitry 315 receives analog or digitalvoice data from microphone 320 or other outgoing baseband data (e.g.,web data, e-mail, interactive video game data) from main processor 340.Transmitter (TX) processing circuitry 315 encodes, multiplexes, and/ordigitizes the outgoing baseband data to produce a processed baseband orIF signal. Radio frequency (RF) transceiver 310 receives the outgoingprocessed baseband or IF signal from transmitter (TX) processingcircuitry 315. Radio frequency (RF) transceiver 310 up-converts thebaseband or IF signal to a radio frequency (RF) signal that istransmitted via antenna 305.

In some embodiments of the present disclosure, main processor 340 is amicroprocessor or microcontroller. Memory 360 is coupled to mainprocessor 340. According to some embodiments of the present disclosure,part of memory 360 comprises a random access memory (RAM) and anotherpart of memory 360 comprises a Flash memory, which acts as a read-onlymemory (ROM).

Main processor 340 executes basic operating system (OS) program 361stored in memory 360 in order to control the overall operation ofwireless subscriber station 116. In one such operation, main processor340 controls the reception of forward channel signals and thetransmission of reverse channel signals by radio frequency (RF)transceiver 310, receiver (RX) processing circuitry 325, and transmitter(TX) processing circuitry 315, in accordance with well-known principles.

Main processor 340 is capable of executing other processes and programsresident in memory 360, such as operations for COMP communications andMU-MIMO communications. Main processor 340 can move data into or out ofmemory 360, as required by an executing process. In some embodiments,the main processor 340 is configured to execute a plurality ofapplications 362, such as applications for CoMP communications andMU-MIMO communications. The main processor 340 can operate the pluralityof applications 362 based on OS program 361 or in response to a signalreceived from BS 102. Main processor 340 is also coupled to I/Ointerface 345. I/O interface 345 provides subscriber station 116 withthe ability to connect to other devices such as laptop computers andhandheld computers. I/O interface 345 is the communication path betweenthese accessories and main controller 340.

Main processor 340 is also coupled to keypad 350 and display unit 355.The operator of subscriber station 116 uses keypad 350 to enter datainto subscriber station 116. Display 355 may be a liquid crystal displaycapable of rendering text and/or at least limited graphics from websites. Alternate embodiments may use other types of displays.

The Multi-user MIMO (MU-MIMO) operation is specified for LTE Release-8system: 3GPP TS 36.211 v 8.8.0, “E-UTRA, Physical channels andmodulation”; 3GPP TS 36.212 v 8.8.0, “E-UTRA, Multiplexing and Channelcoding”; and 3GPP TS 36.213 v8.8.0, “E-UTRA, Physical Layer Procedures”,the contents of each are incorporated by reference. For example, thedemodulation reference signal for the Physical Uplink Shared Channel(PUSCH) is defined in section 5.5.2.1 of E-UTRA, Physical channels andmodulation. In addition, an Uplink (UL) grant is carried using DCIformat as defined in Section 5.3.3.1.1 of E-UTRA, Multiplexing andChannel coding and sections 5.1.1.1, 7.2.1, 7.3 and 8 of E-UTRA,Physical Layer Procedures.

FIG. 4 illustrates separate downlink reference modulation signal (DMRS)sequences with different lengths according to embodiments of the presentdisclosure. The embodiment of the DRMS sequences shown in FIG. 4 is forillustration only. Other embodiments could be used without departingfrom the scope of this disclosure.

In some embodiments, the base station uses a DCI format 0A for UL grantthat allows MIMO transmission in the uplink. The difference of 0A, ascompared to format 0 can include the following. For second codeword, anadditional NDI bit field is included and an additional MCS andredundancy field is included. The resource allocation header isconfigured to indicate type0/type 1 allocation. The resource allocationfield is expanded to allow both type 0 and type 1 allocation. ThePrecoding Matrix Index (PMI)/Rank Indicator (RI) field indicates therank and codeword used in this transmission. The hopping field is onlyuseful for transmissions with low rank up to p, p=1 or 2. BS 102 canconfigure the value of p to SS 116 by higher-layer signaling. Forexample, if p=1, it means SS 116 will only perform hopping when ahopping flag is activated and when the rank of the transmission is “1.”For other ranks, the hopping flags can be reserved for indicating otherstates of the transmission. The 3-bit cyclic shift (CS) field remainsthe same as format 0.

In some embodiments, separately generated DMRS sequences are used forthe different resource segments in the uplink resource allocation. EachDMRS sequence 405, 410 includes the same length as each allocatedsegment 415, 420, and these DMRS sequence are ZC sequences that have thesame group value u, sequence value v. The ZC sequences are UL RSsequences defined in LTE specification E-UTRA, Physical channels andmodulation. SS 116 also will apply the same cyclic shift value n_(DMRS)⁽²⁾ obtained from the 3-bit CS field in the uplink DCI format 0 or 0A,across all the segments, that is, all the segments share the same cyclicshift value. FIG. 4 illustrates a two-segment resource allocation 400.In the example shown in FIG. 4, L1, L2 are the lengths of the twosegments 405, 410. SS 116 reads cyclic shift index CS0 from its UL grantand applies CS0 in both segments 415, 420.

In some embodiments, SS 116 autonomously applies a phase shift on thesecond segment 420 of the resource in order to reduce the overallpeak-to-average power ratio (PAPR) of the transmission.

In some embodiments, separately generated DRMS sequences are used forthe different resource segments in the uplink resource allocation. EachDMRS sequence includes the same length as the allocated segment, andthese DMRS sequence are ZC sequences that have the same group value u,sequence value v. In addition, the segments use different cyclic shiftsand the values of cyclic shifts are derived from the single 3-bit CSfield in the UL grant 0 or 0A according to the following rule (assumeCS0 is signaled in the CS field of DCI format): The first segment 415 isusing CS0, where the first segment 415 is defined as the segment withlowest physical resource block (PRB) indices; the second segment 420,with the second lowest PRB indices, is using CS0+a; the third segment isusing CS0+2a; and so forth.

The value of a can be either fixed or BS 103 can signal the value to SS116 via high-layer signaling in a UE-specific or cell-specific manner.The value “a” can be chosen to maximize the separation of cyclic shiftin different segments. For example, assuming a two-segment allocationand CS0=0 and a=6, then the first segment 415 will use a cyclic shiftvalue of 0, and the second segment 420 will use a cyclic shift value ofCS0+a=6.

In some embodiments, the 3-bit CS field is used to jointly indicate thecyclic shift value and the orthogonal cover code (OCC) index. Thedetailed design is shown in the Table 1 to Table 4 for differenttransmission ranks, and the design is targeting the maximum separationin both CS value and OCC value, in both single user (SU) MIMO and multiuser (MU) MIMO transmissions.

When the transmission rank is R (or R layers are scheduled to betransmitted from SS 116, or a precoding matrix signaled to SS 116 in aUL grant DCI has R columns, where R is an integer), R pairs of UL RSsequences in two SC-FDM symbols in two slots in a subframe are generatedby R pairs of a CS value and an OCC value. These R pairs of a CS valueand an OCC value are determined by the 3-bit field value signaled in aUL grant DCI. When R=1, 2, 3, 4, the 3-bit field value gives the firstpair of a CS value and an OCC value for 1^(st) layer as shown in thesecond and the third row of Table 1, Table 2, Table 3 and Table 4,respectively. The second and later pairs for the 2^(nd) and later layerscorresponding to the 3-bit field value are indicated in the fourth rowof Table 2, Table 3 and Table 4, when R=2, 3, 4.

Table 2, Table 3 and Table 4 for R=2, 3, 4 are constructed by appendingan additional row to the last row of Table 1. The 2^(nd), 3^(rd) and4^(th) pairs of a CS value and an OCC value for R=2, 3, 4 are chosensuch that.

1) when transmission rank is R, CS values are chosen to have maximumseparation within 0, 1 . . . CS_(max), (in 3GPP LTE, CS_(max)=12). Thatis, when the transmission rank is R and the 3-bit field indicates afirst CS n_(CS,1), the other CSs are shown in

Equation 1:

n _(CS,r)=(n _(CS,1) +CS _(max) /R)mod CS _(max) ,r=2,3,K,R.  [EQN. 1]

Furthermore, an OCC paired with a CS n_(CS,r) is found in a same columnas n_(CS,r) is listed in Table 1.

For an MU-MIMO example, if BS 103 schedules two UEs, such as SS 115 andSS 116, each with rank-1 transmission and the CS filed of SS 115 and SS116 are “0” and “1”, respectively, then these SS 115 will use the pairof (CS, OCC)=(0, W0) and SS 116 will use the pair (6, W1), and themaximum separation of 6 is achieved in CS dimension and maximumseparation is also achieved in OCC domain since OCC has switched from W0to W1.

In another SU-MIMO example, if BS 103 is scheduling SS 116 with rank-2transmission, BS 103 can set the CS filed to “0”, then SS 116 will readthe first layer DMRS as pair (CS,OCC)=(0,W0), and the second layer will(implicitly) use the resource associated with the CS field “1”, andthere the pair (CS,OCC)=(6, W1). Again, maximum separation is achievedin this SU-MIMO case.

Table 1 illustrates Mapping from 3-bit CS field to CS and OCC: rank-1.

TABLE 1 3-bit field 0 1 2 3 4 5 6 7 CS 0 6 3 4 2 8 10 9 OCC W0 W1 W0 W1W0 W1 W0 W1

Table 2 illustrates mapping from 3-bit CS field to CS and OCC: rank-2.Here 2^(nd) Resource index refers to the resource pair used by the2^(nd) layer. A value of “1” for the 2^(nd) resource means the (CS, OCC)value is the same as the case when the 3-bit index is 1, that is (CS,OCC)=(6, W1).

TABLE 2 3-bit field (Resource index) 0 1 2 3 4 5 6 7 CS (for 1^(st) 0 63 4 2 8 10 9 layer) OCC (for 1^(st) W0 W1 W0 W1 W0 W1 W0 W1 layer)2^(nd) Resource 1 0 7 6 4 4 3 2 index (for 2^(nd) layer)

Table 3 illustrates mapping from 3-bit CS field to CS and OCC: rank-3.Here 2^(nd) Resource index refers to the resource pair used by the2^(nd) layer. A value of “3” for the 2^(nd) resource means the (CS, OCC)value is the same as the case when the 3-bit index is 3, that is, (CS,OCC)=(4, W1).

TABLE 3 3-bit field (Resource index) 0 1 2 3 4 5 6 7 CS (for 0 6 3 4 2 810 9 1^(st) layer) OCC (for W0 W1 W0 W1 W0 W1 W0 W1 1st layer) 2^(nd)and 3^(rd) 3, 5 4, 6 7 0, 5 1, 6 0, 3 1, 4 2, 1 Resource index (for2^(nd) and 3^(rd) layers)

Table 4 illustrates mapping from 3-bit CS field to CS and OCC: rank-4.Here 2^(nd) Resource index refers to the resource pair used by the2^(nd) layer. A value of “1” for the 2^(nd) resource means the (CS, OCC)value is the same as the case when the 3-bit index is 1, that is (CS,OCC)=(6, W1).

TABLE 4 3-bit field (Resource index) 0 1 2 3 4 5 6 7 CS (for 0 6 3 4 2 810  9 1^(st) layer) OCC (for W0 W1 W0 W1 W0 W1 W0 W1 1^(st) layer)2^(nd), 3^(rd)  1,  0,  0,  4,  3,  3,  3,  0, and 4^(th)  2,  2,  1, 5,  5,  4,  4,  1, Resource 7 7 7 6 6 6 5 2 index (for 2^(nd), 3^(rd)and 4^(th) layers)

That is, a first resource mapping table corresponding to a lowertransmission rank is a subset of a second resource mapping tablecorresponding to a higher transmission rank. For example, resourcemapping Table 1 for rank-1 is a subset (e.g., nested within) resourcemapping Table 2 for rank-2. Further, resource mapping Table 2 for rank-2is a subset (e.g., nested within) resource mapping Table 3 for rank-3;and resource mapping Table 3 for rank-3 is a subset (e.g., nestedwithin) resource mapping Table 4 for rank-4.

In some embodiments, one resource mapping table is used for all ranks ofuplink transmission. This allows BS 102 and SS 116 to implement only onetable for all ranks of uplink transmission. The single resource mappingtable, such as Tables 5-10, is configured such that the lower orderindividual rank tables are nested in the single resource mapping table.

The difference between this approach and the previous approach occurs inthe rank-3 case. In the rank-3 case, the maximum separation among allthree layers no longer holds. The third CS value corresponding to layer3 for a given 3-bit field value when transmission rank is 3, is a CSvalue from those CS values giving maximum separation in CS in a 4 layercase, and is different from the first and the second CS valuescorresponding to layers 1 and 2. Table 4 is re-drawn into Table 5 forease of exposition. Also, the ordering of the DMRS resources used forlayers 2, 3, 4 are slightly different from the previous table. Table 6shows another example, which is slightly different from Table 5 in thatthe 3-bit field indicates CS values only, implying that a UE wouldgenerate DM RS sequences without applying OCCs in two slots.

Table 5 illustrates mapping from 3-bit field to CS and OCC: ranks 1-4.

TABLE 5 3-bit field (Resource index) 0 1 2 3 4 5 6 7 (CS, OCC) 0, 6, 3,4, 1, 7, 10,  9, Layer 1 W0 W1 W0 W1 W0 W1 W0 W1 (CS, OCC) 6, 0, 9, 10, 7, 1, 4, 3, Layer 2 W1 W0 W1 W0 W1 W0 W1 W0 (CS, OCC) 3, 9, 6, 7, 10, 4, 1, 0, Layer 3 W0 W1 W1 W1 W0 W1 W0 W0 (CS, OCC) 9, 3, 0, 1, 4, 10, 7, 6, Layer 4 W1 W0 W0 W0 W1 W0 W1 W1

Table 6 illustrates mapping from 3-bit CS filed to CSs: ranks 1-4.

TABLE 6 3-bit field (Resource index) 0 1 2 3 4 5 6 7 (CS) Layer 1 0 6 34 1 7 10 9 (CS) Layer 2 6 0 9 10 7 1 4 3 (CS) Layer 3 3 9 6 7 10 4 1 0(CS) Layer 4 9 3 0 1 4 10 7 6

Some embodiments include a design with the following rank-dependentcharacteristics:

a) OCC code: for a given 3-bit field value, the OCC code does not changefrom Layer 1 to layer 2, and the OCC code used for layer 3 and layer 4is different from the OCC code used for layer 1&2. The reason for thisdesign is to allow flexible rank 1 and 2 MU-MIMO scheduling, where DMRSorthogonality is maintained when each UE (SS 111-SS 116) can bescheduled with up to rank 2 and the two UEs (SS 115 and SS 116) areallocated non-identical but overlapping PUSCH resources. For example, SS115 and SS 116 are both assigned rank-2 transmission, when SS 115 isassigned the 3-bit field of “1” and SS 116 is assigned a three bit-fieldof “7”.

Therefore:

UE1:Layer 1:(0,W0), Layer 2:(6,W0)

UE2:Layer 1:(9, W1), Layer 2:(3, W1)

In addition, the OCC code separation can ensure good channel estimationperformance for both SS 115 and SS 116.

b) Two alternatives for CS code:

Alt 1: a different set of CS codes is used for layers 3&4, compared tolayers 1&2. Therefore, a total of 4 CS is used in 4 layers.

Alt 2: the same set of CS codes is used for layers 3&4, compared tolayers 1&2, therefore, a total of 2CS issued in 4 layers.

An example design of this embodiment assuming Alt 1 for CS code is shownin Table 7. An example for Alt 2 can be easily obtained by replacing theCS values in layer 3&4 with the CS values in layers 1&2, as shown inTable 8. Table 7 illustrates mapping of 3-bit to CS and OCC resources:rank 1-4. Note the OCC stays the same in layer 1&2, but switches forlayers 3&4. Here Alt 1 of CS code rule is assumed where CS in layers 3&4are different from layers 1&2.

TABLE 7 3-bit field (Resource index) 0 1 2 3 4 5 6 7 (CS, OCC) 0, 6, 3,4, 1, 7, 10,  9, Layer 1 W0 W1 W0 W1 W0 W1 W0 W1 (CS, OCC) 6, 0, 9, 10, 7, 1, 4, 3, Layer 2 W0 W1 W0 W1 W0 W1 W0 W1 (CS, OCC) 3, 9, 6, 7, 10, 4, 1, 0, Layer 3 W1 W0 W1 W0 W1 W0 W1 W0 (CS, OCC) 9, 3, 0, 1, 4, 10, 7, 6, Layer 4 W1 W0 W1 W0 W1 W0 W1 W0

Table 8 illustrates mapping of 3-bit to CS and OCC resources: rank 1-4.In Table 8, the OCC stays the same in layer 1&2, but switches for layers3&4. Here Alt 2 of CS code rule is assumed where CS in layers 3&4 arethe same as layers 1&2.

TABLE 8 3-bit field (Resource index) 0 1 2 3 4 5 6 7 (CS, OCC) 0, 6, 3,4, 2, 8, 10,  9, Layer 1 W0 W1 W0 W1 W0 W1 W0 W1 (CS, OCC) 6, 0, 9, 10, 8, 2, 4, 3, Layer 2 W0 W1 W0 W1 W0 W1 W0 W1 (CS, OCC) 0, 6, 3, 4, 2, 8,10,  9, Layer 3 W1 W0 W1 W0 W1 W0 W1 W0 (CS, OCC) 6, 0, 9, 10,  8, 2, 4,3, Layer 4 W1 W0 W1 W0 W1 W0 W1 W0

In some embodiments, for the SPS scheduled rank-1 transmission or RACHresponse message, if SS 116 is scheduled in Rel-10 transmission, thenn_(DMRS) ⁽²⁾ (the CS value from UL grant discussed herein) shall be setto zero and the OCC shall be set to W0=[11], if there is no PDCCHassociated with the uplink grant for the same transport block and if theinitial PUSCH for the same transport block is semi-persistentlyscheduled. Alternatively, if SS 116 is scheduled in Rel-10 transmission,then n_(DMRS) ⁽²⁾ shall be set to zero and the OCC shall be set toW0=[11], if there is no PDCCH associated with the uplink grant for thesame transport block and if the initial PUSCH for the same transportblock is scheduled by the random access response grant.

In addition, if rank>1 is supported in LTE-A for semi-persistentlyscheduled transmissions, then for each layer, the (CS, OCC) is setaccording to the 3-bit field “0”, either by Table 5, 6 or 7. Forexample, if Table 6 is used, then first layer is fixed as (0,W0), 2^(nd)layer is fixed as (6, W0), and so forth.

In some embodiments, for the SPS scheduled rank-1 transmission or RACHresponse message: if SS 116 is scheduled in Rel-10 transmission,n_(DMRS) ⁽²⁾ (the CS value from UL grant discussed in this document)shall be set to zero, and the OCC shall be set to W, where W belongs tothe set of {W1,W1}, and is signaling by higher layer RRC signaling, ifthere is no PDCCH with DCI format 0 or 0A for the same transport block,and if the initial PUSCH for the same transport block issemi-persistently scheduled, or, if the initial PUSCH for the sametransport block is scheduled by the random access response grant.

Some embodiments include a design with the following rank-dependentcharacteristics:

A) one resource mapping table above is used for all ranks of uplinktransmission. This allows BS 103 and SS 116 to implement only one tablefor all ranks of uplink transmission.

B) For the OCC code: the 8 values are divided into 2 subsets:

For a given 3-bit field value in the first subset (e.g., CSI value in{0, 1, 2, 3}, the OCC code does not change from Layer 1 to layer 2, andthe OCC code used for layer 3 and layer 4 is different from the OCC codeused for layer 1&2.

For a given 3-bit field value in the second subset (e.g., CSI value in{4, 5, 6, 7}), the OCC code does not change from Layers 1 to 3, and theOCC code for layer 4 is different from layers 1 to 3.

The reason for this design is to allow flexible pairing of UEs withdifferent ranks of up to 3, for example pairing of SS 115 with rank-1and SS 116 with rank-3. For example:

SS 115:layer 1:(0, W0), layer 2:(6,W0), layer 3:(9, W0);

SS 116:layer 1: (3,W1).

In addition, the OCC code separation can ensure good channel estimationperformance for both SS 115 and SS 116.

C) Two alternatives for CS code:

1) different set of CS codes is used for layers 3&4, compared to layers1&2. Therefore, a total of 4 CS is used in 4 layers;

2) For ranks 1, 2 the CS separation among layers is 6, for ranks 3, 4the CS separation among layers is 3.

Table 9 illustrates mapping of 3-bit to CS and OCC resources: rank 1-4.(the first 4 entries OCC does not change for layers 1&2, the last 4entries OCC does not change for layers 1, 2, 3).

TABLE 9 3-bit field (Resource index) 0 1 2 3 4 5 6 7 (CS, OCC) 0, 6, 3,4, 2, 8, 10,  9, Layer 1 W0 W1 W0 W1 W0 W1 W0 W1 (CS, OCC) 6, 0, 9, 10, 8, 2, 4, 3, Layer 2 W0 W1 W0 W1 W0 W1 W0 W1 (CS, OCC) 3, 9, 6, 7, 11, 5, 1, 0, Layer 3 W1 W0 W1 W0 W0 W1 W0 W1 (CS, OCC) 9, 3, 0, 1, 5, 11, 7, 6, Layer 4 W1 W0 W1 W0 W1 W0 W1 W0

Some embodiments include a design with the following rank-dependentcharacteristics:

A) one resource mapping table above is used for all ranks of uplinktransmission. This allows BS 103 and SS 116 to implement only one tablefor all ranks of uplink transmission.

For the OCC code: the 8 values are divided into 3 subsets:

1) For a given 3-bit field value in the first subset (e.g., CSI value in{0, 1, 2, 3}, the OCC code does not change from Layer 1 to layer 2, andthe OCC code used for layer 3 and layer 4 is different from the OCC codeused for layer 1&2.

2) For a given 3-bit field value in the second subset (e.g., CSI valuein {4, 5}), the OCC code does not change from Layers 1 to 3, and the OCCcode for layer 4 is different from layers 1 to 3.

3) For a given 3-bit field value in the second subset (e.g., CSI valuein {6, 7}), the OCC code does not change from Layers 1 to 4, or alllayers.

This design enables a flexible pairing of UEs with different ranks of upto 3, for example pairing of SS 115 with rank-1 and SS 116 with rank-3.For example: 1) SS 115:layer 1:(0, W0), layer 2:(6,W0), layer 3:(9, W0);and 2) SS 116:layer 1:(3,W1). In addition, the OCC code separation canensure good channel estimation performance for both UEs.

B) Two alternatives for CS code:

1) A different set of CS codes is used for layers 3&4, compared tolayers 1&2. Therefore, a total of 4 CS is used in 4 layers.

2) For ranks 1, 2 the CS separation among layers is 6, for ranks 3, 4the CS separation among layers is 3.

An example of such a design is shown in Table 10 below. Table 10illustrates mapping of 3-bit to CS and OCC resources: rank 1-4 (thefirst 4 entries OCC does not change for layers 1&2, the next 2 entriesOCC does not change for layers 1, 2, 3, the last 2 entries OCC does notchange for all layers).

TABLE 10 3-bit field (Resource index) 0 1 2 3 4 5 6 7 (CS, OCC) 0, 6, 3,4, 1, 8, 10,  9, Layer 1 W0 W1 W0 W1 W0 W1 W0 W1 (CS, OCC) 6, 0, 9, 10, 7, 2, 4, 3, Layer 2 W0 W1 W0 W1 W0 W1 W0 W1 (CS, OCC) 3, 9, 6, 7, 10, 5, 1, 0, Layer 3 W1 W0 W1 W0 W0 W1 W0 W1 (CS, OCC) 9  3, 0, 1, 4, 11, 7, 6, Layer 4 W1 W0 W1 W0 W0 W1 W0 W1

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

1. For use in a wireless communications network, a base station capableof communicating with a plurality of subscriber stations, the basestation comprising: a transmit path comprising circuitry configured to:transmit control information and data to at least one of the pluralityof subscriber stations in a subframe; transmit a plurality of resourceblocks in the subframe; transmit the data using a subset of antennaports corresponding to a subset of antenna port numbers; map referencesignals corresponding to the subset of antenna ports according to atransmission rank R; and indicate, via a cyclic shift indicator (CSI)field in an uplink grant, an assigned resource index corresponding tothe mapped reference signal, the CSI field comprising a cyclic shift andan orthogonal cover code (OCC) index.
 2. The base station as set forthin claim 1, wherein the transmit path is configured to use a CSI valueto select the cyclic shift and the OCC index based on a resource mappingtable, the resource mapping table is configured to map the cyclic shiftand the OCC index for all transmission ranks R.
 3. The base station asset forth in claim 2, wherein if the CSI value in the uplink grantbelongs to a first subset of CSI values, the OCC index for a firsttransmission layer is the same as an OCC index for a second transmissionlayer, wherein each transmission layer is identified by the transmissionrank, and wherein a size of the first subset varies from 0 to 8, and theOCC index for each of a third transmission layer and a fourthtransmission layer is different than the OCC index for the firsttransmission layer.
 4. The base station as set forth in claim 3, whereina CSI value spacing is 6 within a Transmission Rank R=2 such that theCSI value spacing is maximized between the first transmission layer andsecond transmission layer.
 5. The base station as set forth in claim 3,wherein a CSI value spacing is at least 3 within a Transmission RankR=4.
 6. The base station as set forth in claim 2, wherein if the CSIvalue in the uplink grant belongs to a second subset of CSI values, theOCC index for all transmission layers is the same, wherein eachtransmission layer is identified by the transmission rank, and wherein asize of the third subset varies from 0 to
 8. 7. The base station as setforth in claim 1, wherein the transmit path is configured to use a CSIvalue to select the cyclic shift and the OCC index based on a pluralityof resource mapping table, wherein each of the plurality of resourcemapping tables is associated with a respective transmission rank R. 8.The base station as set forth in claim 7, wherein a first resourcemapping table corresponding to a lower transmission rank is a subset ofa second resource mapping table corresponding to a higher transmissionrank.
 9. For use in a wireless communications network, a subscriberstation capable of communicating with at least one base station, thesubscriber station comprising: a receiver configured to receive controlinformation and data from at least one of the plurality of base stationsin a subframe, wherein the receiver is configured to receive a pluralityof resource blocks in the subframe; and a controller configured to:identify, in a cyclic shift indicator (CSI) field in an uplink grant, anassigned resource index corresponding to a reference signal mappedcorresponding to a subset of antenna ports according to a transmissionrank R, the CSI field comprising a cyclic shift and an orthogonal covercode (OCC) index; and cause the receiver to receive the data using asubset of antenna ports corresponding to a subset of antenna portnumbers and identify the mapped reference signals.
 10. The subscriberstation as set forth in claim 9, further comprising a memory, the memorycomprising a resource mapping table, wherein the controller isconfigured to use the cyclic shift, the OCC index and the transmissionrank to identify the resource index based on the resource mapping table,the resource mapping table is configured to map the cyclic shift and theOCC index for all transmission ranks R.
 11. The subscriber station asset forth in claim 10, wherein if the CSI value in the uplink grantbelongs to a first subset of CSI values, the OCC index for a firsttransmission layer is the same as an OCC index for a second transmissionlayer, wherein each transmission layer is identified by the transmissionrank and wherein a size of the first subset varies from 0 to 8, and theOCC index for each of a third transmission layer and a fourthtransmission layer is different than the OCC index for the firsttransmission layer.
 12. The subscriber station as set forth in claim 11,wherein a CSI value spacing is 6 within a Transmission Rank R=2 suchthat the CSI value spacing is maximized between the first transmissionlayer and second transmission layer.
 13. The subscriber station as setforth in claim 11, wherein a CSI value spacing is at least 3 within aTransmission Rank R=4.
 14. The subscriber station as set forth in claim10, wherein if the CSI value in the uplink grant belongs to a secondsubset of CSI values, the OCC index for all transmission layers is thesame, wherein each transmission layer is identified by the transmissionrank and wherein a size of the third subset varies from 0 to
 8. 15. Thesubscriber station as set forth in claim 9, further comprising a memory,the memory comprising a plurality of resource mapping tables, whereinthe controller is configured to use the cyclic shift, the OCC index andthe transmission rank to identify the resource index, wherein each ofthe plurality of resource mapping tables is associated with a respectivetransmission rank R.
 16. The subscriber station as set forth in claim15, wherein a first resource mapping table corresponding to a lowertransmission rank is a subset of a second resource mapping tablecorresponding to a higher transmission rank.
 17. For use in a wirelesscommunications network, a method of operating a base station capable ofcommunicating with a plurality of subscriber stations, the methodcomprising: transmitting control information and data to at least one ofthe plurality of subscriber stations in a subframe; transmitting aplurality of resource blocks in the subframe; transmitting the datausing a subset of antenna ports corresponding to a subset of antennaport numbers; mapping reference signals corresponding to the subset ofantenna ports according to a transmission rank R; and indicating, via acyclic shift indicator (CSI) field in an uplink grant, an assignedresource index corresponding to the mapped reference signal, the CSIfield comprising a cyclic shift and an orthogonal cover code (OCC)index.
 18. The method as set forth in claim 17, wherein indicatingcomprises using the CSI value to select the cyclic shift and the OCCindex based on a resource mapping table, the resource mapping tableconfigured to map the cyclic shift and the OCC index for alltransmission ranks R.
 19. The method as set forth in claim 18, whereinif the CSI value in the uplink grant belongs to a first subset of CSIvalues, the OCC index for a first transmission layer is the same as anOCC index for a second transmission layer, wherein each transmissionlayer is identified by the transmission rank and wherein a size of thefirst subset varies from 0 to 8, and the OCC index for each of a thirdtransmission layer and a fourth transmission layer is different than theOCC index for the first transmission layer.
 20. The method as set forthin claim 19, wherein a CSI value spacing is 6 within a Transmission RankR=2 such that the CSI value spacing is maximized between the firsttransmission layer and second transmission layer.
 21. The method as setforth in claim 19, wherein a CSI value spacing is at least 3 within aTransmission Rank R=4.
 22. The method as set forth in claim 18, whereinif the CSI value in the uplink grant belongs to a second subset of CSIvalues, the OCC index for all transmission layers is the same, whereineach transmission layer is identified by the transmission rank andwherein a size of the third subset varies from 0 to
 8. 23. The method asset forth in claim 17, wherein indicating comprises using the CSI valueto select the cyclic shift and the OCC index based on a plurality ofresource mapping table, wherein each of the plurality of resourcemapping tables is associated with a respective transmission rank R. 24.The method as set forth in claim 23, wherein a first resource mappingtable corresponding to a lower transmission rank is a subset of a secondresource mapping table corresponding to a higher transmission rank. 25.For use in a wireless communications network, a base station thatcommunicates with subscriber stations, the base station comprising atransmit path configured to: transmit control information and data to atleast one subscriber station in a subframe; transmit a plurality ofresource blocks in the subframe; transmit the data using a subset ofantenna ports corresponding to a subset of antenna port numbers; mapreference signals corresponding to the subset of antenna ports accordingto a transmission rank R; and indicate, via a cyclic shift indicator(CSI) field in an uplink grant, an assigned resource index correspondingto the mapped reference signal, the CSI field comprising a cyclic shiftand an orthogonal cover code (OCC) index, wherein for semi-persistentscheduling of rank-1 transmission or an RACH response message, thecyclic shift value shall be set to zero and the OCC index shall be setto W0=[11], if one of: there is no PDCCH associated with the uplinkgrant for the same transport block and if the initial PUSCH for the sametransport block is semi-persistently scheduled; and there is no PDCCHassociated with the uplink grant for the same transport block and if theinitial PUSCH for the same transport block is scheduled by a randomaccess response grant.
 26. For use in a wireless communications network,a method of operating a base station capable of communicating with aplurality of subscriber stations, the method comprising: transmittingcontrol information and data to at least one of the plurality ofsubscriber stations in a subframe; transmitting a plurality of resourceblocks in the subframe; transmitting the data using a subset of antennaports corresponding to a subset of antenna port numbers; mappingreference signals corresponding to the subset of antenna ports accordingto a transmission rank R; and indicating, via a cyclic shift indicator(CSI) field in an uplink grant, an assigned resource index correspondingto the mapped reference signal, the CSI field comprising a cyclic shiftand an orthogonal cover code (OCC) index, wherein for semi-persistentscheduling of rank-1 transmission or an RACH response message, thecyclic shift value shall be set to zero and the OCC index shall be setto W0=[11], if one of: there is no PDCCH associated with the uplinkgrant for the same transport block and if the initial PUSCH for the sametransport block is semi-persistently scheduled; and there is no PDCCHassociated with the uplink grant for the same transport block and if theinitial PUSCH for the same transport block is scheduled by a randomaccess response grant.